The present invention relates to a progressive distributor, for a central grease and oil lubrication unit, with which lubricant that is supplied under pressure can be delivered to several areas of use. Such a progressive distributor normally comprises several individual sections that are screwed or otherwise connected together and are sealed relative to one another. Each of the individual sections is provided with a piston that is alternately pressed bY the lubricant into its two end positions. With the aid of annular grooves, the pistons are controlled in a certain sequence in such a way that the next piston cannot be displaced until the piston movement of the preceding piston is nearly concluded. All of the piston bores of the individual sections are directly connected by a central bore to an inlet that is supplied via a lubricant line with lubricant that is under an operating pressure of up to about 400 bar.
Each individual section of a progressive distributor is provided with two outlets, so that lubricant supplied thereto can be progressively delivered in a certain sequence and in small, metered quantities to the connected friction locations. After the last friction location has been supplied with lubricant, the lubricating process automatically restarts with the first friction location. If the lubricating process is interrupted at any of the locations by shutdown of the pump or blockage of the pressure line, when the system is reactivated the lubricating process starts again at this location.
For further background with regard to the functioning of a progressive distributor, reference is hereby made to U.S. Pat. No. 3,783,973-Kurten et al, dated Jan. 8, 1974, which patent is being incorporated into this disclosure by this reference thereto.
With the use of such progressive distributors in progressive central lubrication units, it can happen that during the distributor cycle (movement of all pistons to a lubricant discharge position), one or the other lubricating location cannot immediately receive the intended quantity of lubricant. The distributor then maintains a given position in the cycle and is caught in a so-called standstill phase which under certain circumstances can last a long period of time. During this time the other connected friction locations cannot and are not supplied with lubricant, which can lead to inadequate lubrication of these locations. This is particularly true for oil lubrication systems.
Various causes can underlie a delayed delivery of lubricant. For example, lubricating location gaps can temporarily be reduced in size by dirt particles, or system-related problems can temporarily block lubricant inlet bores at the friction locations. This is the case, for example, when due to a momentary load phase of a shaft journal during its rotation in a bearing, the lubricant inlet bore thereof is closed in such a way that not even the operating pressure of the unit is sufficient to free the bore. Although such a blockage is only temporary due to the movement of the shaft, it nonetheless leads to a standstill of the distributor cycle.
It is therefore an object of the present invention, while avoiding the aforementioned drawbacks, to improve a progressive distributor for central grease and oil lubrication units in such a way that even where the delivery of lubricant to one or more areas of use is delayed in time, the cyclical operation is not adversely affected and the delivery of lubricant to the disrupted area of use is made possible at a later point in time.